Low-Ash Lubricating Oils for Diesel Engines

ABSTRACT

The lubricant for a sump-lubricated, compression-ignited engine may contain an amount of a C12-C24 carboxylic acid-based fuel additive or component obtained by migration from the fuel. Good lubricant performance is obtained by including in the lubricant a boron-containing additive in an amount to provide about 2 to about 500 ppm B to the lubricant, provided that the total sulfated ash level is less than 0.8 weight percent.

BACKGROUND OF THE INVENTION

The disclosed technology relates to a lubricant for a sump-lubricated internal combustion engine.

In recent years, fuel additives based upon fatty acids derived from both plant and animal sources have been introduced into the market as ashless lubricity improvers or as biodiesel fuel. For example, the presence of one or more ashless lubricity improvers is often desirable in low-sulfur fuels. One major type of ashless lubricity improvers includes fatty acids and their amide or ester derivatives. Biodiesel fuel refers to the use of lower alkyl esters of fatty acids as a portion, typically 2-20%, or up to 100%, of the fuel itself. As an engine is operated, significant amounts of such a fuel, as well as additives and other materials included within the fuel, may enter or migrate into the lubricant crankcase via “blow-by” from the cylinder, due to imperfect sealing by the piston rings or by other mechanisms. The residence time of hydrocarbon fuel itself in the crankcase is typically short as it readily volatilizes and escapes by normal crankcase ventilation. However, both gasoline and diesel fuel may contain a variety of performance additives, including lubricity improvers, as well as bio-diesel fuel components, which typically comprise heavier molecules than those of the hydrocarbon fuel itself. As a result, such materials tend not to escape the crankcase so readily but, rather, build up in concentration in the lubricant. During a typical drain oil interval, up to 2% of additives or other components from the fuel can accumulate in the lubricant.

At the same time, there is a continuing desire to provide lubricants for internal combustion engines with reduced phosphorus content or reduced metal content as measured by sulfated ash (ASTM D 874). This desire is largely motivated by the fact that, while such materials may be quite useful in the lubricant, they may, in a similar manner, make their way into the exhaust stream. Phosphorus and metals in the exhaust, in turn, are believed to interfere with pollution control devices such as exhaust catalyst systems or particulate filters. It is desirable, under these real-world operating conditions, to provide a lubricant having good performance characteristics, including good deposit control.

Conventional lubricants, with comparatively high levels of additives that contribute phosphorus or sulfated ash, are normally quite satisfactorily balanced to provide good lubrication and deposit control. However, current or future lubricants containing lower levels of phosphorus (e.g., <0.06%) and sulfated ash (e.g., <0.80%) may require more sophisticated balancing of additives. This is also the case when they contain or are expected to contain various fuel additives or components based on fatty acids derived from animal or plants.

We have now found that certain components that normally have little or no effect, when used in conventional lubricants that contain fuel additive or component, have beneficial effects when used in low ash, low phosphorus versions of the formulation that also contain fuel additive or component based on fatty acids derived from animal or plants.

SUMMARY OF THE INVENTION

The disclosed technology provides a method for lubricating a sump-lubricated, compression-ignited engine which is fueled by a liquid fuel containing a fatty acid-based fuel additive or component, wherein said fatty acid-based fuel additive or component is susceptible to or does migrate into the lubricant in the sump of said engine, said method comprising supplying to said engine a lubricant which comprises: (a) an oil of lubricating viscosity; and (b) a boron-containing additive in an amount to provide 2 to 500 ppm B to the lubricant; said lubricant having a total sulfated ash level (ASTM D 874) of less than about 0.8 weight percent.

The disclosed technology further provides lubricant comprising (a) an oil of lubricating viscosity; (b) a boron-containing additive in an amount to provide about 2 to about 500 ppm B to the lubricant; (c) about 0.5 to about 5 percent by weight of fatty acid-based fuel additive or component (typically as accumulated from the fuel) comprising a mixture of fatty acids having about 14 to about 22 carbon atoms or a condensation product or salt thereof; said lubricant having a total sulfated ash level of less than about 0.8 weight percent.

DETAILED DESCRIPTION OF THE INVENTION

Various preferred features and embodiments will be described below by way of non-limiting illustration.

The amount of each chemical component described is presented exclusive of any solvent or diluent oil, which may be customarily present in the commercial material, that is, on an active chemical basis, unless otherwise indicated. However, unless otherwise indicated, each chemical or composition referred to herein should be interpreted as being a commercial grade material which may contain the isomers, by-products, derivatives, and other such materials that are normally understood to be present in the commercial grade.

One element of the present technology is an oil of lubricating viscosity. Such oils include natural and synthetic oils, oil derived from hydrocracking, hydrogenation, and hydrofinishing, unrefined, refined, re-refined oils or mixtures thereof. A more detailed description of unrefined, refined and re-refined oils is provided in International Publication W02008/147704, paragraphs [0054] to [0056]. A more detailed description of natural and synthetic lubricating oils is provided in paragraphs [0058] to [0059] respectively of W02008/147704. Synthetic oils may also be produced by Fischer-Tropsch reactions and typically may be hydroisomerized Fischer-Tropsch hydrocarbons or waxes. In one embodiment oils may be prepared by a Fischer-Tropsch gas-to-liquid synthetic procedure as well as other gas-to-liquid oils.

Oils of lubricating viscosity may also be selected from any of the base 15 oils in Groups I-V as specified in the American Petroleum Institute (API) Base Oil Interchangeability Guidelines. The five base oil groups are as follows: Group I: >0.03% sulfur and/or <90% saturates and viscosity index 80 to 120; Group II: ≦0.03% S and ≧90% saturates and VI 80 to 120; Group III: ≦0.03% S and ≧90% saturates and VI >120; Group IV: all polyalphaolefins; Group V: all others. Groups I, II and III are typically referred to as mineral oil base stocks.

The amount of the oil of lubricating viscosity present is typically the balance remaining after subtracting from 100 wt % the sum of the amount of the compound of the invention and the other performance additives.

The lubricating composition may be in the form of a concentrate and/or a fully formulated lubricant. If the lubricating composition of the invention (comprising the additives disclosed hereinabove) is in the form of a concentrate which may be combined with additional oil to form, in whole or in part, a finished lubricant), the ratio of the of these additives to the oil of lubricating viscosity and/or to diluent oil include the ranges of 1:99 to 99:1 by weight, or 80:20 to 10:90 by weight.

The lubricating composition is susceptible to containing, or will in fact contain, fatty acid-based fuel additive or component of the type typically found in a liquid fuel. In one embodiment, the material may be a fuel component such as a biodiesel fuel compound. In another embodiment the material may be a fuel additive such as a lubricity improver. The various descriptions of the present technology may be applied to lubricants containing fatty acid-based fuel additive or alternatively to lubricants containing fatty acid-based fuel component. When the fuel additive is a lubricity improver, the lubricity improver may comprise a mixture of fatty acids having 14 to 22 carbon atoms or a condensation product or salt thereof, e.g., an ester, amide, or imide derivative thereof. A common lubricity improver of this type is tall oil fatty acid (TOFA), which is a mixture of naturally occurring fatty acids that are refined from tall oil. Tall oil is a mixture of saturated and unsaturated fatty and rosin acids (that is, C₁₄ to C₂₂ fatty acids or mixtures thereof), which is obtained in paper pulp manufacture when the pulping is done by the sulfate process. Tall oil is further separated into tall oil heads and tall oil fatty acid. Tall oil fatty acids typically are a mixture of fatty acids, predominately oleic and linoleic, containing residual rosin acids or resin acids, such as abietic acid and its isomers.

Other fatty acids or mixtures of fatty acids may also be employed, including such acids as lauric, myristic, palmitic, margaric, stearic, linolenic, arachidic, gadoleic, behenic, erucic, and lignoceric acids. The acids may be saturated or unsaturated (with one, two or three sites of unsaturation), linear or branched. Oleic and linoleic acids are linear acids of 18 carbon atoms having 1 or 2 sites of unsaturation, respectively.

The term “fatty acids” may generally refer to individual or mixed C12-C24 carboxylic acids, and, more particularly, to individual or mixed C12-C24 alkyl or alkenyl carboxylic acids. The C12-C24 or C14-C22 or C16-C18 acids and mixtures thereof that are typically used may be obtained from a variety of sources beside tall oil. Other oils which provide appreciable amounts of such acids include cocoa butter, corn oil, cottonseed oil, lard, olive oil, palm oil, peanut oil, rapeseed oil, canola oil, safflower oil, soybean oil, and sunflower oil.

The acids may also be present, in whole or in part, as condensation products or salts. Condensation products include esters, amides, and imides. Esters include lower alkyl esters such as methyl, ethyl, and propyl; and in one embodiment the fatty acid-based fuel additive or component comprises a methyl ester of a C12-24 acid. Esters also include glycerides (mono-, di-, or tri-), which would be characteristic of incomplete saponification of a source oil. Salts include metal salts, amine salts, and ammonium salts, where common metals may include alkali or alkaline earth metals such as sodium, potassium, magnesium, or calcium, as well as transition metals such as iron, titanium, molybdenum, or zinc, any of which may be intentionally present or may be present as a result of interaction of the acid with metallic species present in a fuel or lubricant.

The fatty acid-based fuel additive or component may be present in the lubricant, resulting from migration from the fuel or otherwise, in an amount of 0.1 or 0.3 or 0.5 to 5 percent by weight, or 0.8 to 4 percent or 1 to 3 percent or 1.5 to 2.5 percent by weight, e.g., about 2 percent by weight.

The lubricants of the present technology will also contain a boron-containing additive in an amount to provide 2 to 500 parts per million by weight (ppm) boron to the lubricant. Other suitable amounts of boron include 10 to 400 ppm or 30 to 300 ppm or 50 to 200 ppm or 60 to 150 ppm or 70 to 100 ppm. The actual amount of the boron-containing additive will, of course, depend on the boron content of the additive. In certain embodiments, the amount of the boron-containing additive or additives will be 0.1 to 4 percent by weight, based on the amount of the lubricant, and in other embodiments 0.5 to 3.5 or 1 to 3 percent by weight.

One suitable boron-containing additive is a borated dispersant. A borated dispersant is a dispersant that has been treated or reacted with a borating agent such as boric acid to incorporate boron into the detergent structure, whether by chemical bonding or by physical interaction.

Dispersants are well known in the field of lubricants and include what are known as ashless-type dispersants and polymeric dispersants. Ashless type dispersants are characterized by a polar group attached to a relatively high molecular weight hydrocarbon chain. Typical ashless dispersants include nitrogen-containing dispersants such as N-substituted long chain alkenyl succinimides, also known as succinimide dispersants. Succinimide dispersants are more fully described in U.S. Pat. Nos. 4,234,435 and 3,172,892. Another class of ashless dispersant is high molecular weight esters, prepared by reaction of a hydrocarbyl acylating agent and a polyhydric aliphatic alcohol such as glycerol, pentaerythritol, or sorbitol. Such materials are described in more detail in U.S. Pat. No. 3,381,022. Another class of ashless dispersant is Mannich bases. These are materials which are formed by the condensation of a higher molecular weight, alkyl substituted phenol, an alkylene polyamine, and an aldehyde such as formaldehyde and are described in more detail in U.S. Pat. No. 3,634,515. Other dispersants include polymeric dispersant additives, which are generally hydrocarbon-based polymers which contain polar functionality to impart dispersancy characteristics to the polymer. Dispersants can also be post-treated by reaction with any of a variety of agents beside boron compounds. Among these are urea, thiourea, dimercaptothiadiazoles, carbon disulfide, aldehydes, ketones, carboxylic acids, hydrocarbon-substituted succinic anhydrides, nitriles, epoxides, and phosphorus compounds.

Dispersants, and in particular N-substituted long chain alkenyl succinimide dispersants, may be borated using a variety of agents selected from the group consisting of the various forms of boric acid (including metaboric acid, HBO₂, orthoboric acid, H₃BO₃, and tetraboric acid, H₂B₄O₇), boric oxide, boron trioxide, and alkyl borates. In one embodiment the borating agent is boric acid which can be used alone or in combination with other borating agents. The borate dispersant can be prepared by blending the boron compound and the N-substituted long chain alkenyl succinimide and heating them at a suitable temperature, typically 80° C. to 250° C., such as 90° C. to 230° C. or 100° C. to 210° C., until the desired reaction has occurred. The molar ratio of the boron compounds to the dispersant may be 10:1 to 1:4, or 4:1 to 1:3, or 1:2. An inert liquid can be used in performing the reaction, such as toluene, xylene, chlorobenzene, dimethylformamide, or mixtures thereof. Processes for making borated dispersants and their use in lubricating compositions are disclosed in U.S. Pat. Nos. 3,087,936 and 3,254,025. The amount of boron contained within a borated dispersant may be, in some embodiments, 0.5 to 5 weight percent, or 1 to 5 wt. %, or 1.5 to 4 wt. %, or 2 to 4 wt. %, or 2.5 to 3 weight percent.

Alternatively, the boron compound may be a borate ester, which term includes borated epoxides. The borate ester may be prepared by the reaction of a boron compound (a borating agent as described above) and at least one compound selected from epoxy compounds, alcohols, and mixtures thereof. Typically the alcohols include monohydric alcohols, dihydric alcohols, trihydric alcohols or higher alcohols. Borated epoxides can be prepared by reacting, at a temperature from 80° C. to 250° C., boric acid or boron trioxide with at least one epoxide which in certain embodiments may contain at least 8 carbon atoms, for oil solubility. Other borate esters, such as borated fatty acid esters, include esters based on alcohols including glycerol, prepared by reacting the borating agent with the alcohol (which may likewise optionally contain at least 8 carbon atoms) at appropriate temperatures and times, removal of the water of reaction. In certain embodiments, there is sufficient boron present such that each boron will react with from 1.5 to 2.5 hydroxyl groups present in the reaction mixture.

In the case of a borated dispersant containing about 2.8 weight percent boron (active chemical basis, excluding diluent oil), a suitable amount of material to be present in the lubricant may be or 0.03 to 1.4 weight percent or 0.1 to 0.8 weight percent or 0.2 to 0.4 weight percent. Corresponding amounts for other materials containing different amounts of boron may be readily calculated.

As used herein, the term “hydrocarbyl substituent” or “hydrocarbyl group” is used in its ordinary sense, which is well-known to those skilled in the art. Specifically, it refers to a group having a carbon atom directly attached to the remainder of the molecule and having predominantly hydrocarbon character. Examples of hydrocarbyl groups include: hydrocarbon substituents, including aliphatic, alicyclic, and aromatic substituents; substituted hydrocarbon substituents, that is, substituents containing non-hydrocarbon groups which, in the context of this invention, do not alter the predominantly hydrocarbon nature of the substituent; and hetero substituents, that is, substituents which similarly have a predominantly hydrocarbon character but contain other than carbon in a ring or chain. A more detailed definition of the term “hydrocarbyl substituent” or “hydrocarbyl group,” including permissible amounts of other atoms, is found in paragraphs [0118] to [0119] of International Publication W02008 147704.

Additional conventional components may be used in preparing a lubricant according to the present technology, for instance, those additives typically employed in a crankcase lubricant. Crankcase lubricants may typically contain any or all of the following components hereinafter described.

The composition may, for instance, contain a dispersant other than a borated dispersant. The description of dispersants suitable for boration, as described above, is also an applicable description of non-borated dispersants. The amount of any non-borated dispersant may in certain embodiments be up to 8 percent by weight, e.g. 0.1 to 8 percent, or 0.5 to 7, or 1 to 6, or 3 to 5 percent.

Another common component is a detergent. Detergents are commonly overbased materials, otherwise referred to as overbased or superbased salts, which are generally single phase, homogeneous Newtonian systems characterized by a metal (e.g., Na, K, Mg, Ca, Ba) content in excess of that which would be present for neutralization according to the stoichiometry of the metal and the particular acidic organic compound reacted with the metal. The overbased materials are prepared by reacting an acidic material (typically an inorganic acid or lower carboxylic acid, preferably carbon dioxide) with a mixture comprising an acidic organic compound, a reaction medium comprising at least one inert, organic solvent (mineral oil, naphtha, toluene, xylene, etc.) for said acidic organic material, a stoichiometric excess of a metal base, and a promoter such as a phenol or alcohol. The acidic organic material will normally have a sufficient number of carbon atoms to provide a degree of solubility in oil. The amount of excess metal is commonly expressed in terms of metal ratio. The term “metal ratio” is the ratio of the total equivalents of the metal to the equivalents of the acidic organic compound. A neutral metal salt has a metal ratio of one. A salt having 4.5 times as much metal as present in a normal salt will have metal excess of 3.5 equivalents, or a ratio of 4.5. Such overbased materials are well known to those skilled in the art. Patents describing techniques for making basic salts of sulfonic acids, carboxylic acids, phenols, phosphonic acids, and mixtures of any two or more of these include U.S. Pat. Nos. 2,501,731; 2,616,905; 2,616,911; 2,616,925; 2,777,874; 3,256,186; 3,384,585; 3,365,396; 3,320,162; 3,318,809; 3,488,284; and 3,629,109.

Other detergents include salixarate detergents. These include overbased materials prepared from salicylic acid (which may be unsubstituted) with a hydrocarbyl-substituted phenol, such entities being linked through —CH₂— or other alkylene bridges. It is believed that the salixarate derivatives have a predominantly linear, rather than macrocyclic, structure, although both structures are intended to be encompassed by the term “salixarate.” Salixarate derivatives and methods of their preparation are described in greater detail in U.S. Pat. No. 6,200,936 and PCT Publication WO 01156968.

Overbased detergents are often characterized by Total Base Number (TBN). TBN is the amount of strong acid needed to neutralize all of the over-based material's basicity, expressed as potassium hydroxide equivalents (mg KOH per gram of sample). Since overbased detergents are commonly provided in a form which contains a certain amount of diluent oil, for example, 40-50% oil, the actual TBN value for such a detergent will depend on the amount of such diluent oil present, irrespective of the “inherent” basicity of the overbased material. For the purposes of the present invention, the TBN of an overbased detergent is to be recalculated to an oil-free basis. Detergents which are useful in the present invention may have a TBN (oil-free basis) of 50 to 800 or 100 to 800, and in one embodiment 150 to 750, and in another, 400 to 700. If multiple detergents are employed, the overall TBN of the detergent component (that is, an average of all the specific detergents together) may be in the above ranges.

In certain embodiments, the lubricants of the present technology may contain a metal-containing salicylate detergent, such as an overbased calcium hydrocarbyl-substituted salicylate detergent. The salicylate detergent may have a Total Base Number of 100 to 700, or 200 to 700, or 200 to 600, or 250 to 400, calculated on an oil-free basis. The amount of the salicylate detergent, if present, may be 0.05 to 1.5 weight percent, or 0.1 to 1, or 0.3 to 0.8 weight percent. Salicylate detergents are well known; see, e.g., U.S. Pat. No. 5,688,751 or 4,627,928.

Another component is an antioxidant. Antioxidants encompass phenolic antioxidants, which may comprise a butyl substituted phenol containing 2 or 3 t-butyl groups. The para position may also be occupied by a hydrocarbyl group or a group bridging two aromatic rings. They may also contain an ester group at the para position, for example, an antioxidant of the formula

wherein R³ is a hydrocarbyl group such as an alkyl group containing, e.g., 1 to 18 or 2 to 12 or 2 to 8 or 2 to 6 carbon atoms; and t-alkyl can be t-butyl. Such antioxidants are described in greater detail in U.S. Pat. No. 6,559,105. Antioxidants also include aromatic amines, such as nonylated diphenylamines. Other antioxidants include sulfurized olefins, titanium compounds, and molybdenum compounds. U.S. Pat. No. 4,285,822, for instance, discloses lubricating oil compositions containing a molybdenum and sulfur containing composition. Typical amounts of antioxidants will, of course, depend on the specific antioxidant and its individual effectiveness, but illustrative total amounts can be 0.01 to 5 percent by weight or 0.15 to 4.5 percent or 0.2 to 4 percent. Additionally, more than one antioxidant may be present, and certain combinations of these can be synergistic in their combined overall effect.

Viscosity improvers (also sometimes referred to as viscosity index improvers or viscosity modifiers) may be included in the compositions of this invention. Viscosity improvers are usually polymers, including polyisobutenes, polymethacrylic acid esters, hydrogenated diene polymers, polyalkylstyrenes, esterified styrene-maleic anhydride copolymers, hydrogenated alkenylarene-conjugated diene copolymers and polyolefins. Multifunctional viscosity improvers, which also have dispersant and/or antioxidancy properties are known and may optionally be used. Viscosity improvers may be used at, e.g., 0.1 to 0.8 percent or 0.3 to 0.6 percent by weight.

Another additive is an antiwear agent. Examples of anti-wear agents include phosphorus-containing antiwear/extreme pressure agents such as metal thiophosphates, phosphoric acid esters and salts thereof, phosphorus-containing carboxylic acids, esters, ethers, and amides; and phosphites. The present technology is particularly useful for formulations in which the total amount of phosphorus as delivered by, e.g., the antiwear agent, does not exceed 0.12%. Suitable amounts may include 0.005 to about 0.10 percent by weight or 0.01 to 0.08 percent or 0.02 to 0.05 percent. Often the antiwear agent is a zinc dialkyl-dithiophosphate (ZDP). For a typical ZDP, which may contain 10 percent P (calculated on an oil free basis), suitable amounts may include 0.05 to 0.6 or 0.05 to 0.55 or 0.1 to 0.5 or 0.2 to 0.5 percent by weight. Non-phosphorus-containing anti-wear agents, which may also be used, include borate esters (including borated epoxides), dithiocarbamate compounds, molybdenum-containing compounds, and sulfurized olefins.

Other materials that may be used as antiwear agents include tartrate esters, tartramides, and tartrimides. Examples include oleyl tartrimide (the imide formed from oleylamine and tartaric acid) and oleyl diesters (from, e.g, mixed C12-16 alcohols). Other related materials that may be useful include esters, amides, and imides of other hydroxy-carboxylic acids in general, including hydroxy-polycarboxylic acids, for instance, acids such as tartaric acid, citric acid, lactic acid, glycolic acid, hydroxy-propionic acid, hydroxyglutaric acid, and mixtures thereof. These materials may also impart additional functionality to a lubricant beyond antiwear performance. These materials are described in greater detail in US Publication 2006-0079413 and PCT publication WO2010/077630. Such derivatives of (or compounds derived from) a hydroxy-carboxylic acid, if present, may typically be present in the lubricating composition in an amount of 0.1 weight % to 5 weight %, or 0.2 weight % to 3 weight %, or greater than 0.2 weight % to 3 weight %.

Other additives that may optionally be used in lubricating oils include pour point depressing agents, extreme pressure agents, anti-wear agents, color stabilizers and anti-foam agents.

It is known that some of the materials described above may interact in the final formulation, so that the components of the final formulation may be different from those that are initially added. For instance, metal ions (of, e.g., a detergent) can migrate to other acidic or anionic sites of other molecules. The products formed thereby, including the products formed upon employing the composition of the present invention in its intended use, may not be susceptible of easy description. Nevertheless, all such modifications and reaction products are included within the scope of the present technology; the present technology encompasses the composition prepared by admixing the components described above.

The present technology is particularly useful also when the total sulfated ash of a lubricant is relatively low, for instance, less than 1%, or less than 0.8%, e.g., 0.01 to 0.8, or 0.1 to 0.75, or 0.2to 0.7, or 0.25 to 0.6 percent. It is also useful in formulations that are relatively low in phosphorus, such as less than 0.11 percent, or less than 0.10 percent, e.g., 0.01 to 0.10 or 0.02 to 0.08 or 0.03 to 0.07 percent.

EXAMPLES

A series of test lubricant formulations is prepared. Each formulation includes, in addition to the specific materials mentioned in the table below, the following materials, which are held constant in one of two formulations:

(A) High ash formulation (Sulfated Ash level >1.0% wt): containing one or more of each of an olefin copolymer viscosity modifier, a succinimide dispersant, a dispersant-viscosity modifier, an antioxidant blend, an overbased calcium detergent, a zinc dialkyldithiophosphate, and a pour point depressant, in a mineral oil.

(B) Low ash formulation (Sulfated Ash level <0.8% wt): Containing the same formulation as (A) but with reduction in ash containing overbased detergent and zinc dialkyldithiophosphate components.

In the lubricant formulations are included the following additional materials (in both formulations the phosphorus content is about 0.1 wt. %):

High Ash (>1%) Low Ash (<0.8%) Amounts, % Ex 1* Ex 2* Ex 3* Ex 4 TOFA content(a) 2 2 2 2 Borated dispersant, con- 0 0.45 0 0.45 taining 2.8% B (oil free) KHT Deposits 0.5 0.5 1.0 1.5 Panel Coker Rating 50 47 50 54 *A comparative or reference example (a)Tall oil fatty acid.

As indicated in the above table, the lubricant formulations are evaluated by the KHT (Komatsu Hot Tube) Deposits test and the Panel Coker test. The Komatsu hot tube test (280° C.) consists of glass tubes which are inserted through and heated by an aluminum heater block. The test sample is pumped via a syringe pump through the glass tube for 16 hours, at a flow rate of 0.31 cm³/hr, along with an air flow of 10 cm³/min. At the end of the test the tubes are rinsed and rated visually on a scale of 0 to 10, with 0 being a black tube and 10 being a clean tube. In the Panel Coker deposit test, the sample, at 105° C., is splashed for 4 hours on an aluminum panel maintained at 325° C. The aluminum plates are analyzed using image analysis techniques to obtain a universal rating. The rating score is based on “100” being a clean plate and “0” being a plate wholly covered in deposit.

The results show that, in a conventional, high-ash lubricating oil containing fuel additive, the presence of the boron-containing component has no effect or even a slightly negative effect on deposit control. However, in a low ash version of the same lubricating oil containing fuel additive, the presence of the boron-containing component has an unexpected beneficial effect on deposit control.

Each of the documents referred to above is incorporated herein by reference. The mention of any document is not an admission that such document qualifies as prior art or constitutes the general knowledge of the skilled person in any jurisdiction. Except in the Examples, or where otherwise explicitly indicated, all numerical quantities in this description specifying amounts of materials, reaction conditions, molecular weights, number of carbon atoms, and the like, are to be understood as modified by the word “about.” It is to be understood that the upper and lower amount, range, and ratio limits set forth herein may be independently combined. Similarly, the ranges and amounts for each element of the invention can be used together with ranges or amounts for any of the other elements. As used herein, the expression “consisting essentially of’ permits the inclusion of substances that do not materially affect the basic and novel characteristics of the composition under consideration. 

1. A method for lubricating a sump-lubricated, compression-ignited engine which is fueled by a liquid fuel containing fatty acid-based fuel additive or component, wherein said fatty acid-based fuel additive or component is susceptible to or does migrate into the lubricant in the sump of said engine, said method comprising supplying to said engine a lubricant which comprises: (a) an oil of lubricating viscosity; (b) a boron-containing additive in an amount to provide about 2 to about 500 ppm B to the lubricant; and (c) an overbased detergent having a TBN (oil free basis) of at least 400; said lubricant having a total sulfated ash level of less than about 0.8 weight percent.
 2. The method of claim 1 wherein the fatty acid-based fuel additive or component comprises a fatty acid or a condensation product or salt thereof.
 3. The method of claim 1 wherein the fatty acid-based fuel additive or component comprises a methyl ester of a C12-24 acid.
 4. The method of claim 1 wherein the fatty acid-based fuel additive or component comprises a mixture of fatty acids having about 14 to about 22 carbon atoms.
 5. The method of claim 1 wherein the fatty acid-based fuel additive or component comprises tall oil fatty acids.
 6. The method of claim 1 wherein the fatty acid-based fuel additive or component is present in the lubricant, resulting from migration from the fuel, in an amount of about 0.5 to about 5 percent by weight.
 7. The method of claim 1 wherein the boron-containing additive comprises a borated dispersant.
 8. The method of claim 7 wherein the borated dispersant comprises a borated succinimide dispersant containing about 0.5 to about 5 weight percent boron (oil free basis).
 9. The method of claim 1 wherein the amount of the boron-containing additive is about 0.1 to about 4 percent by weight.
 10. The method of claim 1 wherein the sulfated ash level of the lubricant is about 0.2 to less than about 0.8 weight percent.
 11. The method of claim 1 wherein the phosphorus content of the lubricant is less than about 0.12 percent by weight.
 12. A lubricant comprising (a) an oil of lubricating viscosity; (b) a boron-containing additive in an amount to provide about 2 to about 500 ppm B to the lubricant; (c) an overbased detergent having a TBN (oil free basis) of at least 400; and (d) about 0.5 to about 5 percent by weight of a fatty acid-based fuel additive or component comprising a mixture of fatty acids having about 14 to about 22 carbon atoms or a condensation product or salt thereof. said lubricant having a total sulfated ash level of less than about 0.8 percent.
 13. A composition prepared by admixing the components of claim
 12. 14. The composition of claim 13 wherein the admixing of the components occurs within an internal combustion engine and arises from operation of said engine.
 15. The composition of claim 14 wherein said internal combustion engine is a compression-ignited engine comprising a lubricant sump.
 16. The method of claim 1 wherein the amount of the fatty acid-based fuel additive or component is about 0.1 to about 3 percent by weight.
 17. The lubricant of claim 12 wherein the amount of the fatty acid-based fuel additive or component is about 0.5 to about 3 percent by weight.
 18. A lubricant comprising (a) an oil of lubricating viscosity; (b) a boron-containing additive in an amount to provide about 2 to about 500 ppm B to the lubricant; and (c) about 0.5 to about 3 percent by weight of a fatty acid-based fuel additive or component comprising a mixture of fatty acids having about 14 to about 22 carbon atoms or a condensation product or salt thereof; said lubricant having a total sulfated ash level of less than about 0.8 percent. 